This invention relates to electronic circuits, and more particularly, to oscillator circuits.
Oscillator circuits are very important in modern electronics. Oscillators are used to generate periodic waveforms and may have a wide variety of applications. These applications may include the generation of clock signals for synchronous electronic systems (e.g., computer systems), generation of a mixing signal for conversion of a signal to another frequency band in a radio receiver, or generation of a carrier signal upon which information may be transmitted. Countless other examples exist as well.
Oscillator circuits are subject to various problems. In some oscillator circuits, it is difficult to sustain oscillation over a wide variation in temperature, devices process variation and frequency. Another problem with oscillator circuits is that it may sometimes be difficult to obtain a stable state upon initialization.
Various types of oscillator circuits have been designed to cope with the problems discussed above. However, often times these circuits require excess current consumption to insure operation over all required conditions.
An oscillator circuit is disclosed. In one embodiment, the oscillator includes a trans-conductance circuit, an envelope detector, and an amplitude comparison circuit.
The trans-conductance circuit (or more generally, a gain circuit) is configured to amplify a periodic signal produced by a crystal. Amplitude peaks of the periodic signal may be detected in the envelope detector, which may determine an average amplitude value based on the detected peaks. The average amplitude value may be compared to a DC voltage value in the amplitude comparison circuit. The DC voltage value may include both a DC average of the periodic signal as well as a predetermined DC offset value. The amplitude comparison circuit may generate a feedback signal responsive to the comparison. The trans-conductance circuit may adjust the level of amplification of the periodic signal based on the feedback signal in order to ensure that the oscillator produces a periodic output signal at a desired level. The periodic signal may be provided as an output through an output stage.
A method for producing a periodic output signal includes first producing a periodic signal with a crystal. The periodic signal may be amplified by a trans-conductance circuit, and an average amplitude value of the periodic signal may be determined. The average amplitude value of the periodic circuit may be compared to a DC voltage value, wherein the DC voltage value is the sum of a DC average value of the periodic signal and a predetermined DC offset voltage value. Responsive to the comparison, a feedback signal may be generated and provided through a feedback loop to the trans-conductance circuit. The trans-conductance circuit may adjust the level of amplification provided to the periodic signal responsive to the feedback signal. The periodic signal may be received by an output stage which buffers the signal and provides a periodic output signal.